Teprotumumab Divergently Alters Fibrocyte Gene Expression: Implications for Thyroid-associated Ophthalmopathy.

CONTEXT: Teprotumumab, an IGF-I receptor (IGF-IR) inhibitor, is effective in thyroid-associated ophthalmopathy (TAO). The drug can modulate induction by TSH of IL-6 and IL-8 in CD34+ fibrocytes and their putative derivatives, CD34+ orbital fibroblasts (CD34+ OF). Fibrocytes express multiple thyroid autoantigens and cytokines implicated in TAO, which are downregulated by Slit2. Inflammation and disordered hyaluronan (HA) accumulation occur in TAO. Whether teprotumumab alters these processes directly in fibrocytes/CD34+ OF remains uncertain.

OBJECTIVE: Determine teprotumumab effects on expression/synthesis of several TAO-relevant molecules in fibrocytes and GD-OF.

DESIGN/SETTING/PARTICIPANTS: Patients with TAO and healthy donors were recruited from an academic endocrine and oculoplastic practice.

MAIN OUTCOME MEASURES: Real-time PCR, specific immunoassays.

RESULTS: Teprotumumab attenuates basal and TSH-inducible autoimmune regulator protein, thyroglobulin, sodium iodide symporter, thyroperoxidase, IL-10, and B-cell activating factor levels in fibrocytes. It downregulates IL-23p19 expression/induction while enhancing IL-12p35, intracellular and secreted IL-1 receptor antagonists, and Slit2. These effects are mirrored by linsitinib. HA production is marginally enhanced by teprotumumab, the consequence of enhanced HAS2 expression.

CONCLUSION: Teprotumumab affects specific gene expression in fibrocytes and GD-OF in a target-specific, nonmonolithic manner, whereas IGF-IR control of these cells appears complex. The current results suggest that the drug may act on cytokine expression and HA production systemically and locally, within the TAO orbit. These findings extend our insights into the mechanisms through which IGF-IR inhibition might elicit clinical responses in TAO, including a potential role of Slit2 in attenuating inflammation and tissue remodeling.